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Instroduction to Astrophysics of Cosmic Rays

Instroduction to Astrophysics of Cosmic Rays. Igor V. Moskalenko ( stanford/kipac ). There is nothing new to be discovered in physics now. All that remains is more and more precise measurement. — Lord Kelvin, 1900. Goals. To give an overview of astrophysics of cosmic rays

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Instroduction to Astrophysics of Cosmic Rays

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  1. Instroduction toAstrophysics of Cosmic Rays Igor V. Moskalenko (stanford/kipac)

  2. There is nothing new to be discovered in physics now. All that remains is more and more precise measurement. — Lord Kelvin, 1900 Goals • To give an overview of astrophysics of cosmic rays • To show the place of recent data in the overall picture • Target audience: particle and high-energy physicists • Organization • A bit of history • General information on CRs • Understanding CR propagation (models) • New data • Instrumentation • Conclusion

  3. An experiment in nature, like a text in the Bible, is capable of different interpretations, according to the preconceptions of the interpreter. — William Jones,1781 • There is no deficit in explanations of the PAMELA positron excess (Adriani+08): >370 papers since Oct 2008! • Various species of the dark matter (most of papers) • Pulsars • SNRs • Microquasars • a GRB nearby • … • Perhaps we have to discuss a deficit of positrons, not their excess! • Unfortunately, >99.7% of these explanations are wrong • …Because there is only one correct explanation

  4. One Good Experiment is Worth Thousand Theories… • ATIC electrons: >270 citations (in ~1 yr) • PPB-BETS electrons: >150 citations (in ~1 yr) • Fermi LAT electrons: >170 citations (in <1 yr) • HESS electrons: >100 citations (in <1 yr) • PAMELA positron fraction: >370 citations (in ~1 yr) • PAMELA antiprotons: >150 citations (in <1 yr) • BESS program (only journal papers): ~1000 citations Of course, most of citations are coming from particle physics ★ using NASA ADS

  5. A Particle Physicist’s View (pre ~2000) • An Astronomer does stamp collecting • An Astrophysicist does engineering • A Particle physicist does fundamental science • .....we have been humbled! − PersisDrell TeV Particle Astrophysics 2009 Page 5

  6. Summary Thoughts • Wealth of data and excitement • This is a healthy field! • Multiwavelength/Multimessager/Multicultural • We are bold in our aspirations! • Will be a rich field for decades to come • Astrophysics is an essential part of Particle Physics!! − PersisDrell TeV Particle Astrophysics 2009 Page 6

  7. 100 Years of Cosmic Rays 1912 Victor Hess, an Austrian scientist, took a radiation counter (a simple electroscope) on a balloon flight He rose to 17,500 feet (without oxygen) and measured that the amount of radiation increases as the balloon climbed Nobel Prize: 1936

  8. W.Bothe C. Anderson H.Yukawa C.Powell Early Discoveries of New Particles in CRs 1929 Bothe (Nobel Prize 1954) and Kolhorster verified that the cloud chamber tracks were curved. Thus the cosmic radiation was charged particles 1932 a discovery of positron by C. Anderson (Nobel Prize 1936) 1937 a discovery of muonby Neddermeyer & Anderson and simultaneously by Street & Stevenson 1947 pionspredicted by Yukawa (1935, Nobel Prize 1949) to explain the force that binds the nucleus together were discovered (C. Powell et al.; Nobel Prize 1950) kaonswere discovered by Rochester & Butler

  9. Renaissance of Particle Astrophysics Particle astrophysics, which has recently emerged as an interdisciplinary science, is flourishing nowadays. It was born in the early days of cosmic-ray physics about a century ago and then reborn twice, first with the launch of the first X-ray telescopes, and second with the discovery that the matter in the universe is dominated by something dark, the dark matter. The latter rebirth brought an army of particle physicists into astrophysics, while astrophysicists began to realize that supersymmetry can play a role on a macro scale. Particle astrophysics is now a busy intersection between high-energy astrophysics, particle physics, and cosmology.

  10. General information on CRs

  11. All Particle CR Spectrum This is an astonishing observation! • All particle CR spectrum is almost featureless. It can be described as a single power-law with index -3 in >12 decades in energy and >32 decades in intensity! • There are only 3 well-established features: • the knee • the ankle • GZK cutoff • Alot of information is hidden in the spectra and abundances of individual CR species: nuclear isotopes, antiprotons, electrons, positrons (+diffuse gamma rays) • CRs are the only probes of the interstellar materialavailable to us. • The whole physics is involved: various branches of Astrophysics, MHD, shock waves, plasma physics, atomic, nuclear, & particle physics, exotic physics – SUSY… Galactic Galactic+extragalactic GZK cutoff extragalactic

  12. Positrons and antiprotons constitute a tiny fraction of the total CR flux, yet may contain signatures of new physics!

  13. Spectra of CR nuclei Examples of spectra of individual elements in cosmic rays

  14. Elemental abundances in CRs and in the Solar System A lot of information is hidden in elemental and isotopic abundances of CR. The elements which are rare in the solar system, such as Li, Be, B, Sc, Ti, V, and some others, appear to be abundant in CRs. They are called “secondaries” because they are produced by spallations of heavier nuclei (so-called “primary”, e.g. C, O, Fe) during the CR propagation. The CR age deduced from the amount of secondaries is ~10 Myr. “Output”: CR abundances (ACE) Si CNO Fe “sec.” “secondary” “prim.” “primary” Al F Cl LiBeB CrMn ScTiV “Input”: solar system abundances

  15. Heavy Nuclei in CRs Heavy nuclei are produced in SN explosions. They can’t propagate from large distances because of the very large inelastic cross section. Wiedenbeck+2007

  16. Isotopic Data Atomic number Very detailed isotopic data exist at low energies! (Isotopes of the same element are connected by lines) ACE data ACE: 100-200 MeV/nucleon Solar System Wiedenbeck+2001

  17. Fermi-LAT 1-year Gamma-Ray Skymap Galactic plane ~80% of gamma-rays are produced by CR interactions with interstellar gas and radiation field! – therefore, the diffuse Galactic gamma rays trace CR proton and electron spectra throughout the Galaxy Sources

  18. A theory is something nobody believes, except the person who made it. An experiment is something everybody believes, except the person who made it. − Albert Einstein To make sense of all these data, one needs a model!

  19. Transport Equation…

  20. SNR RX J1713-3946 42 sigma (2003+2004 data) Chandra B HESS HESS PSF π 0 e e e e π π Fermi gas gas _ _ + + + + + + - - - - - - P P CRs in the Interstellar Medium ISM X,γ synchrotron IC ISRF P He CNO •diffusion •energy losses •reacceleration •convection •production of secondaries bremss WIMP annihil. X,γ • P, p Flux LiBeB He CNO 20 GeV/n BESS • CR species: • Only 1 location • modulation ACE PAMELA helio-modulation

  21. Halo Gas, sources CR Propagation: the Milky Way Galaxy Optical image: Cheng et al. 1992, Brinkman et al. 1993 Radio contours: Condon et al. 1998 AJ 115, 1693 100 pc NGC891 40 kpc 0.1-0.01/ccm 1-100/ccm Sun 4-12 kpc Intergalactic space R Band image of NGC891 1.4 GHz continuum (NVSS), 1,2,…64 mJy/ beam “Flat halo” model (Ginzburg & Ptuskin 1976)

  22. Dark Matter (p,đ,e+,γ) - Nuclear component in CR: What we can learn? Nucleo- synthesis: supernovae, early universe, Big Bang… Stable secondaries: Li, Be, B, Sc, Ti, V Propagation parameters: Diffusion coeff., halo size, Alfvén speed, convection velocity… Radio (t1/2~1 Myr): 10Be, 26Al, 36Cl, 54Mn K-capture: 37Ar,49V, 51Cr, 55Fe, 57Co Energy markers: Reacceleration, solar modulation Extragalactic diffuse γ-rays: blazars, relic neutralino Short t1/2 radio 14C & heavy Z>30 Local medium: Local Bubble Solar modulation Heavy Z>30: Cu, Zn, Ga, Ge, Rb Material & acceleration sites, nucleosynthesis (r-vs. s-processes)

  23. A Model of CR Propagation in the Galaxy • Gas distribution (energy losses, π0, brems) • Interstellar radiation field (inverse Compton, e±energy losses) • Isotopic & particle production cross sections • Gamma-ray production: brems, inverse Compton, π0 • Energy losses: ionization, Coulomb, brems, IC, synch • Solve transport equations for all CR species • Fix propagation parameters • Then we a ready for “precise” Astrophysics: • background for indirect DM searches and other exotics • propagation of the DM signal • CR fluxes in distant locations • Galactic/extragalactic diffuse gamma-ray emission (extragalactic emission may also contain signatures of exotic physics) • background for astrophysical gamma-ray sources • studies of the origin of CRs and interstellar medium

  24. Transport Equations ~90 (no. of CR species) sources (SNR, nuclear reactions…) ψ(r,p,t) – density per total momentum diffusion convection (Galactic wind) diffusive reacceleration (diffusion in the momentum space) E-loss radioactive decay fragmentation + boundary conditions

  25. How It Works: Fixing Propagation Parameters Radioactive isotopes: Galactic halo size Zh Boron/Carbon (B/C) Carbon E2 Flux Be10/Be9 Interstellar Ek, GeV/nucleon Ek, MeV/nucleon Zh increase • Using secondary/primary nuclei ratio (B/C) & flux: • Diffusion coefficient and its index • Propagation mode and its parameters (e.g., reacceleration VA, convection Vz) • Propagation parameters are model-dependent • Make sure that the spectrum is fitted as well Ek, MeV/nucleon Parameters (model dependent): D~ 1028 (ρ/1 GV)α cm2/s α≈ 0.3-0.6 Zh ~ 4-6 kpc VA ~ 30 km/s

  26. Discrimination of the propagation models • Different propagation models are tuned to fit the low energy part of sec./prim. ratio where the accurate data exist • The sharp peak at ~1 GeV/nucleon has been confirmed by Pamela ACE Ulysses Voyagers Reacceleration Standard diffusion B/C • However, the differ at high energies which will allow to discriminate between them when more accurate data will be available CREAM Ahn+’08

  27. Secondary/Primary Nuclei Ratio Being tuned to one type of secondary/primary ratio (e.g. B/Cratio) the propagation model should be automatically consistent with all secondary/primary ratios: • sub-Fe/Fe • He3/He4 • pbar/p B/C Jones+’01 Sub-Fe/Fe

  28. Importance of the Pbar/P Ratio • Similarly to other secondary/ primary ratios, pbar/p ratio can be used to derive the propagation parameters • Different ratios probe different volumes in the Galaxy with the pbar/p ratio probing the largest volume since the pbar inelastic cross section is ~40 mb (vs. ~270 mb for Carbon, vs. ~750 mb for Iron) • The interstellar spectrum of pbars can be calculated because of the production threshold is large vs. the injection spectra of other nucleons which are assumed • Therefore, it can be used to probe interstellar spectrum of protons, solar modulation, and, of course, to search for signatures of exotic physics Abe+’08

  29. Importance of the Pbar/P Ratio (Cont’ed) • Systematic measurements of pbars in CRs (BESS) allow us to study heliospheric modulation and charge-sign effects • Important also for e+/e ratio Abe+’08

  30. Nuclear Reaction Network + Cross Sections Many different isotopes in CRs are produced via spallations of heavier nuclei: A+(p,He)→B*+X “stable” isotopes Secondary, radioactive ~1 Myr & K-captureisotopes Co57 Fe55 Mn54 Cr51 V49 Ca41 Ar37 Cl36 β-, n Al26 p,EC,β+ Plus some dozens of more complicated reactions But many cross sections are not well known… Be7 Be10 p n

  31. natSi+p26Al ST W 27Al+p26Al W ST Effect of Cross Sections: Radioactive Secondaries Different size from different ratios… In determination of the propagation parameters one has to take into account: • Errors in CR measurements (@ HE & LE) • Errors in production cross sections • Errors in the lifetime estimates T1/2=? W – Webber+ ST – Silberberg & Tsao - - - – measured Zhalo,kpc • The error bars can be significantly reduced if more accurate cross sections are used • Different ratios provide consistent parameters

  32. Components of the ISM: Views from the Inside synchrotron 21 cm H I 2.6 mm CO (H2) dust stars & star forming optical n-stars, BHs CRs x gas

  33. Z=0, R=0 kpc 4 kpc 8 kpc 12 kpc 16 kpc optical IR CMB ISRF: Large Scale Distribution • Requires extensive modelling: • Distribution of stars of different stellar classes in the Galaxy • Dust emission • Radiative transfer • The z scale height is large, takes 10s of kpc at R = 0 kpc to get to level of CMB Total Optical IR CMB R = 0,4,8,12,16kpc Energy Density Optical + IR (no CMB)

  34. Gas distribution in the Milky Way Molecular hydrogen H2is traced using J=1-0 transition of 12CO, concentrated mostly in the plane (z~70 pc, R<10 kpc) Atomic hydrogen H I(traced by 21 cm emission line) has a wider distribution (z~1 kpc, R~30 kpc) Ionized hydrogen H II – small proportion, but exists even in halo (z~1 kpc) Sun

  35. 20 0 -20 -40 Galactic Latitude 220 200 180 160 140 120 100 80 60 40 20 CfA 1.2m Galactic Longitude Carbon Monoxide (CO) maps • Extend CO surveys to high latitudes • newly-found small molecular clouds will otherwise be interpreted as unidentified sources, and clearly limit dark matter studies • C18O observations (optically thin tracer) of special directions (e.g. Galactic center, arm tangents) • assess whether velocity crowding is affecting calculations of molecular column density, and for carefully pinning down the diffuse emission Dame, Hartmann, & Thaddeus (2001) Dame & Thaddeus (2004)

  36. Calculation of the Gas Distribution • Neutral interstellar medium – most of the interstellar gas mass • 21-cm H I & 2.6-mm CO (surrogate for H2) • Differential rotation of the Milky Way – plus random motions, streaming, and internal velocity dispersions – is largely responsible for the spectrum • Rotation curveV(R)  unique line-of-sight velocity-Galactocentric distance relationship • This is the best – but far from perfect – distance measure available • Column densities: N(H2)/WCO ratio assumed; a simple approximate correction for optical depth is made for N(H I); self-absorption of H I remains CO Rotation Curve Dame+’01 H I Clemens (1985) Kalberla+’05 W. Keel

  37. More on gas in the Milky Way Surface mass density of the H2 in M sun pc−2 Sun No velocity information No velocity information Near-far ambiguity Pohl+’08 Contours of line-of-sight velocities from differential rotation of the Milky Way

  38. New Experiments The Reason of making Experiments is, for the Discovery of the Method of Nature, in its Progress and Operations. − Robert Hooke, 1664

  39. Antiproton to proton ratio • Pbar/p ratio by PAMELA is consistent with previous measurements by BESS • Consistent with predictions of propagation models - most of pbars are secondary produced by CRs preliminary Adriani+’09 • Provide a serious restriction on DM WIMP candidates Picozza’09

  40. Antiproton Spectrum Measurements of the absolute pbar flux are more important than the ratio Also consistent with BESS data and predictions of the propagation models Testifies that most antiprotons are secondary produced by CR interactions with interstellar gas preliminary Picozza’09 26/06/2009 40

  41. Kobayashi+’03 Early Measurements of CR Electrons • Early measurements have shown that the spectrum of CR electrons is steeper than that of protons • Predictions of possible spectral features @ HE associated with local SNR

  42. Electron Fluctuations/SNR Stochastic Events GALPROP/Credit S.Swordy 100 TeV electrons GeV electrons Bremsstrahlung Electron energy loss timescale: 1 TeV: ~300 kyr 100 TeV: ~3 kyr Compare with CR lifetime ~10 Myr E(dE/dt)-1,yr Ionization IC, synchrotron Coulomb 107 yr Energy losses 106 yr 1 GeV 1 TeV 1MeV

  43. What’s here? Latronico+’09

  44. Interpretation of CR Electron Data • CR electron spectrum is consistent with a single power-law with index -3.05 • Can be reproduced well by the propagation models • Multi-component interpretation is also possible • Dark matter contribution • Nearby sources (SNR, pulsars) • … • The key in understanding of the electron spectrum is the origin of the positron excess and the diffuse gamma-ray emission

  45. PAMELA Positron Fraction sec. production (GALPROP) Solar modulation Adriani+’08 • The excess in positron fraction is confirmed and extended to higher energies while regular propagation models predict a decrease at HE • Low-energy behavior is expected due to the charge-sign dependent solar modulation • Perhaps the most intriguing puzzle! • There is no deficit in explanations (Dark Mattervs.regular Astrophysical sources) • More accurate data including at HE are necessary

  46. EGRET: The famous GeV-ray excess • Physical phenomena? • Dark Matter? • Instrumental artifact? Strong+’00,’04

  47. Fermi/LAT: Diffuse emission at mid-latitudes • Conventional GALPROP model is in agreement with the LAT data at mid-latitudes (mostly local emission) • This means that we understand the basics of cosmic ray propagation and calculate correctly interstellar gas and radiation field model Abdo+’09

  48. Fermi/LAT: Diffuse γ-ray Emission from the Local Gas • The spectrum of the local gas, after the subtraction of the IC emission, agrees well with the model • Confirms that the local proton spectrum is similar to that from direct measurements Abdo+’09

  49. Morphology of the Diffuse Emission @ 150 GeV IC π0 Conventional Dark Matter IC π0 Regis&Ullio’09

  50. Milagro: TeV Observations of Fermi Sources Many γ-ray sources show extended structures at HE – thus they are also the sources of accelerated particles (CRs) unID (new TeV source) Fermi Pulsar MGRO 1908+06 HESS 1908+063 unID (new TeV source) Geminga pulsar Milagro C3 Radio pulsar (new TeV source) SNR IC433 MAGIC, VERITAS G.Sinnis’09 Pulsar (AGILE/Fermi) MGRO 2019+37 Fermi Pulsar SNR gCygni Fermi Pulsar HESS, Milagro, Magic Fermi Pulsar Milagro (C4) 3EG 2227+6122 Boomerang PWN G65.1+0.6 (SNR) Fermi Pulsar (J1958) New TeV sources SNR W51 HESS J1923+141

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